This invention relates to a method of waterproofing a wire harness in which a grommet-passing portion of a wire bundle for passing through a grommet, adapted to be mounted in a through hole in a vehicle body panel of an automobile, is tied into a waterproof structure in which a gap between any two adjacent wires is closed by a water stop agent.
FIGS. 6A, 6B and 6C show a related method of producing a waterproof wire harness.
The wire harness 1 is used in the electric wiring for an automobile, and when a group of wires are shaped into an arrangement form, corresponding to an arrangement form on the vehicle, a waterproofing is applied to those portions of the wires which are to be passed through a grommet 3 adapted to be mounted in a through hole formed in a vehicle body panel.
More specifically, first, the grommet 3 is mounted on a predetermined portion of the wire bundle 4 as shown in FIG. 6A. Then a water stop agent in an unsolidified state is filled in a gap between an inner face of a harness-passing hole 3a in the grommet 3 and the wire bundle 4 as shown in FIG. 6B, and is allowed to stand for a predetermined period of time, so that the water stop agent is solidified, thereby providing a waterproof structure in which the gap between the wire bundle 4 and the grommet 3 is filled up by the solidified water stop agent 6, as shown in FIG. 6C.
In such a producing method, however, a very small gap remains between any two adjacent wires at the grommet-passing portion of the wire bundle 4, and therefore there is a fear that external rain water intrudes into these gaps because of a capillary phenomenon, which has invited a problem that a sufficient waterproof effect can not be obtained.
Therefore, there has been proposed a producing method shown in FIGS. 7 to 8F.
The waterproof wire harness-producing method is disclosed in JP-A-10-135657. A waterproofing jig 13 is beforehand mounted on a predetermined portion of an arrangement plate 11 which is used for preforming or shaping a group of wires into an arrangement form corresponding to an arrangement form on a vehicle.
A plurality of wire group support jigs 15a, 15b, 15c, 15d, 15e, . . . for supporting the wire group in a branched pattern, corresponding to the predetermined arrangement form, are mounted on the arrangement plate 11.
The waterproofing jig 13 has slits 13c for arranging the wires of the grommet-passing portion in a row, each of the slits being formed by a pair of opposed arms 13a and 13b. 
The width of the slit 13c is so determined as to arrange the wires of the grommet-passing portion vertically one upon another in one row.
The waterproof structure of the grommet-passing portion, utilizing the waterproofing jig 13, is formed according to the procedure of FIGS. 8A to 8F.
First, grommet-passing portions of the group of wires 16 are arranged vertically in a row in a plane by the pair of spaced-apart slits 13, as shown in FIG. 8A. Then, a water stop agent 19 in an unsolidified state is applied to one face of that portion of the arranged wire group 16, disposed between the pair of slits 13c, by a water stop agent-coating nozzle 18 as shown in FIG. 8B. Generally, moisture-curing silicone RTV is used as the water stop agent 19. Then, a band of film 21 for uniting purposes is bonded to the one face of the wire group 16, coated with the water stop agent 19, thereby interconnecting the wires of the wire group 16 in such a manner that these wires are kept arranged in one row, and thereafter the waterproofing jig 13 is moved downward, thereby removing the wire group 16 from the waterproofing jig 13, as shown in FIG. 8C.
Then, the band of film 21 is wound on the wire group 16 to tie this wire group into a wire bundle of a round cross-section, as shown in FIG. 8D. Further, a tape 23 is wound on that portion of the wire bundle, tied by the band of film 21, thereby forming the wire bundle into such a circular cross-sectional shape that the wire bundle can be snugly fitted into a harness-passing hole in a grommet, as shown in FIG. 8E, and the water stop agent is solidified. Thereafter, the grommet 25 is mounted on that portion of the wire bundle having the tape 23 wound thereon, as shown in FIG. 8F.
In the above waterproof wire harness-producing method, however, in the case where the wire group includes wires of different outer diameters, it is difficult to arrange the wires in one row, and besides it is difficult to coat the water stop agent.
When the arrangement of the wires and the coating of the water stop agent are effected satisfactorily, a gap between any two adjacent wires at the grommet-passing portion of the wire bundle can be filled up by the water stop agent. Even in such a case, however, when the group of wires 16 is tied into a bundle by the band of film 21, the outer diameter of the resulting wire bundle is liable to vary, and in the next step of winding the tape 23, the outer diameter of the wire bundle must be corrected into a size, corresponding to the diameter of the harness-passing hole in the grommet 25, by adjusting the amount of winding of the tape 23. Thus, the operation for adjusting the amount of winding of the tape 23 is required, and therefore there is problems that much time and labor are required for the operation, and that it is difficult to carry out the operation in an automated manner.
And besides, when the tape 23 is wound spirally, there is a fear that very small gaps are formed in step portions, formed by the overlapping portions of the wound tape 23, thus lowering the waterproof performance.
It is therefore an object of the present invention to provide a method of waterproofing a wire harness in which grommet-passing portions of a group of wires can be tied together into a waterproof structure in which interstices between the wires are filled by a water stop agent, and besides the bundle of tied wires can be highly precisely finished into a desired outer diameter without the need for a time-consuming tape-winding operation regardless of whether or not the wire bundle includes the wires of different outer diameters, and the improved productivity and the enhanced waterproof performance can be achieved.
In order to achieve the above object, according to the present invention, there is provided a method of waterproofing a plurality of wires which constitute a wire harness passed through a through hole formed in a grommet, comprising the steps of:
providing a lower mold having a first recessed portion, and a upper mold having a second recessed portion, the first recessed portion and the second recessed portion defining a cavity when the upper mold and the lower mold are integrated, such that a cross section of the cavity is substantially identical with a cross section of the through hole formed in the grommet;
placing the wires on the first recessed portion of the lower mold;
coating the wires with water stop agent;
applying vibration to the wires so as to permeate the water stop agent into a gap between the wires;
integrating the upper mold and the lower mold such that a cross section of the wire harness is matched with a cross section of the cavity; and
solidifying the water stop agent permeated into the wires.
Preferably, the cross section of the cavity is shaped into a circle. Preferably, a cross section of the first recessed portion of the lower mold is identical with a part of an inner peripheral face of the through hole formed in a grommet.
In the above construction, a grommet-passing portion of the wire harness permeated into a gap between the wires with the water stop agent, is pressed and formed into the cross sectional shape, corresponding to the cross sectional shape of the through hole of the grommet, so that the gaps between the wires are filled with the water stop agent. Further, by the press-shaping operation of integrating the upper mold and lower mold, the wire group is formed into the wire bundle of high precision which has such an outer diameter as to snugly fit in the harness-passing hole in the grommet.
Therefore, the grommet-passing portion of the wire group can be easily tied into the waterproof structure in which the gaps between the wires are filled up by the water stop agent, and besides the tied wire bundle can be highly precisely finished into the desired outer diameter without the need for a time-consuming tape-winding operation regardless of whether or not the wire bundle includes the wires of different outer diameters, and the production process can be suitably automated, and the improved productivity and the enhanced waterproof performance can be achieved.
Preferably, the water stop agent has a low viscosity. In this case, as compared with the case where there is used a water stop agent of relatively high viscosity, the water stop agent, coated on the wire group in the water stop agent-coating step, can easily permeate into the gap between any two adjacent wires during the shaking operation in the water stop agent-penetrating step, and therefore there can be obtained the good condition in which the water stop agent sufficiently permeates into the gap between any two adjacent wires in a short time. Therefore, the lowered reliability of the waterproof performance due to variations in the penetration of the water stop agent can be prevented, and besides the time, required for the water stop agent-penetrating step, can be shortened.